The term particle spectrometer naturally refers to an instrument that produces some type of spectrum associated with particles, essentially a histogram of some characteristic, such as speed, kinetic energy, mass (i.e., mass spectrometer), size, or shape. They are used in many sciences, and in astronomy, one or more may be present on a space mission such as an interplanetary explorer.
The typical type of space-mission particle spectrometer aims to classify particles by speed, kinetic energy, and/or mass. They may aim to observe the solar wind, the interplanetary medium, or outgassing from planets or moons. They share technology used in radiation detectors.
Some are aimed specifically at charged particles, which have the advantage that magnets and electric fields may be used to direct them, focus them, or sort them by momentum or charge. This can be used to filter the particle stream so as to detect a specific type of particle, e.g., alpha particles or beta particles, and may also be used to steer away the charged particles, allowing neutral particles to be observed, e.g., free neutrons.
Kinetic energy can be determined by directing them at a semiconductor detector (i.e., solid state detector or SSD) that produces a pulse that varies according to the particle's KE. Speed can be determined by detecting the particle's presence in a pair of points along its flight path (time-of-flight spectrometer or TOF spectrometer) such as directing it through a thin width of material that will emit electrons as the particle passes through. The instrument may carry out both measurements, allowing particle mass to be inferred.